Synthesis and characterization of nickel-N-heterocyclic carbenes linked to a calix[6]arene platform and their applications in Suzuki-Miyaura cross-coupling catalysis

Metallocalix[n]arenes in catalysis: A 13-year update

“…dehalogenated product. Remarkably, Ni/97 systems proved better performing than benchmark catalysts based on other phosphines such as PPh 3 , P(o-tolyl) 3 and the Buchwald-type phosphane o-biph-PPh 2 .With respect to larger calixarene platforms, Ni complexes of N-heterocyclic carbenes (NHCs) bound to a calix[6]arene scaffold were recently disclosed by Chetcuti et al (Figure30)[104]. These compounds were tested in the Suzuki-Miyaura coupling of PhB(OH) 2 with 4-X-acetophenone ( X = Cl, Br) in toluene at 100 °C in the presence of K 3 PO 4 as a base.…”

Supramolecular Catalysts for Organic Synthesis: Preparation and Applications of Cyclodextrins and Calixarenes in C−C Cross‐Coupling Reactions

“…Similarly, in 2020 Chetcuti and co-workers reported the preparation of NHC-functionalized calix [6]arenes complexes with nickel and their evaluation in the Suzuki reaction; in this case, the NHC moiety was attached to the lower rim of a 1,3,5-trimethoxy-p-tertbutylcalix [6] via methylene spacers. [74] In a similar path, Brenner, Matt and co-workers developed calix[4]arenes substituted by one or two adjacent imidazolium moieties (Scheme 24, 63 and 70, respectively), as published in 2011. [75] Calix[4]arene 63 was obtained from the initial tribenzylation of 58 to generate 59, which next underwent an iodination step with trichloroisocyanuric acid (TCIA) and sodium iodide to furnish 60 (Scheme 24a).…”

“…It was inferred that the role of the calixarenes in this case was the microsolubilization of hydrophobic substrates via the formation of host‐guest complexes and the activation of the base via complexation of the counter‐anion. Similarly, in 2020 Chetcuti and co‐workers reported the preparation of NHC‐functionalized calix[6]arenes complexes with nickel and their evaluation in the Suzuki reaction; in this case, the NHC moiety was attached to the lower rim of a 1,3,5‐trimethoxy‐ p ‐ tert butylcalix[6] via methylene spacers [74] …”

Design Concepts for N-Heterocyclic Carbene Ligands

“…These complexes have been applied in reactions including: Suzuki cross-coupling reactions in aqueous solution (where traditional NHCs may yield poorly soluble complexes) [89], Heck reactions [86], and copper-catalysed azide-alkyne cycloadditions [90]. In a study of Suzuki-Miyaura coupling catalysed by a calix [6]arene complex containing three nickel centres it was shown that the best results were obtained using the complexes in which the nickel centres are closest to the calix [6]arene rim [91].…”